Methods for the analysis of genetic polymorphism have found wide utility in basic research, clinical diagnostics, forensics, and other areas. One particularly useful method of detecting genetic polymorphism is based on variations in the length of repeat sequences, such methods being variously referred to as short tandem repeat analysis (STR), variable number of tandem repeat analysis (VNTR), minisatellite analysis, and microsatellite analysis.
Detection of length polymorphisms in nucleic acid repeat sequences has up to now relied on gel electrophoresis for the determination of the length of the repeat sequence. However, gel electrophoresis has several important drawbacks in the context of repeat sequence length polymorphism analysis. First, molecular length measurements based on electrophoretic mobility are inherently imprecise due to a complicated relationship between molecular size and electrophoretic mobility. Second, the degree to which the electrophoretic process can be multiplexed is limited by the number of electrophoresis lanes and by the size of different loci run in a single lane, i.e., loci must be selected which do not electrophoretically co-migrate.